Slow Acceleration / Reduced Top Speed - 1981 DD 8V71

[lostagain]

An electric fuel pump in line between the tank and the primary filter primes the system really easily.

JC

[luvrbus]

The filter base has a plug to remove for priming that is where I prime the system from

[Geoff]

Well, it sounds like you still have issues.  It is normal to have to hold the throttle high to keep the engine running after changing the fuel filters even after putting clean fuel in them.

It is not normal to get air in the fuel system after being parked.  So either your fuel filters are loose, or the fuel line(s) are loose or damaged letting air get in the system.

You shouldn't have to prime the system if everything is right. However, a permanently mounted electric fuel pump with a bypass is the easiest back-up system to have.

For now, make sure the filters aren't loose (don't overtighen!), and the fuel lines are tight.

[HenryTX]

Well, it turns out this issue may not yet be resolved after all.
Took the bus out yesterday to head to a nearby state park, and it was slow to accelerate, again. Absolute top speed was 60 on flat parts, though I had to "pedal to the metal" to get her there.
On slight inclines, it wouldn't do more than 40, and it had to down shift to do that, even.

Looking back on the performance improvement a month ago, the only change that was made was a new set of fuel filters and some Sea Foam in a quarter tank of diesel. I assume this provided a general cleaning to the fuel lines/tank/injectors, etc, that could have been partially clogged by gunk from the fuel tank.

Is it possible that having sat unused for 1 month that the fuel system components gunked up again?
Would a few more cans of Sea Foam fix this up?
Could the fuel injectors be dirty/malfunctioning? The fuel pump?

I look forward to your troubleshooting ideas!

[Geoff]

Your muffler could be plugged up (falling apart inside or full of oil), and creating so much back pressure the engine can't get full power.

[buswarrior]

No more shotgun parts changing, snake oil drinking...

Methodically confirm the proper mechanical operation of the throttle linkage.

That the injectors go to full fuel when the accelerator is pushed to the floor. Bent rods, rusted attachment points that bend when you push the pedal up front, "adjustments" inadvertently made to external connections on the governor...

Check under the driver's floor, with an assistant, every rod, crank, linkage, attachment point, bracket, hanger... same down the back...

If a cable install, a split shield somewhere will allow movement at the pedal, without pushing the throttle down the back.

The busnut who plumbs a pair of fuel pressure gauges into the filter heads doesn't guess about plugged filters EVER again, he just looks at the gauges and compares to spec/each other.

And KNOW, not guess.

Make the coach work FOR you, not against you.

Seafoam isn't fixing what's wrong here...

Happy coaching!
Buswarrior

[neoneddy]

Was it cold?   Could fuel starting to gel slow fuel filter flow?  I know parts of TX can get in the 30s or lower.  I took mine out a few weeks ago, and I felt like before enough fuel ran through the engine to warm it up I wasn't going as fast as I'd like.

[HenryTX]

So, I'm finding this is an inconsistent issue, which is perplexing.
The latest theory is that the drastic temperature changes here in SE Texas are causing water to build up in the fuel tank.
For example, when I run the engine on a cold day, there may be some water created during diesel circulation.

Has anyone else ever dealt with water in their fuel tank before?
What's an effective way to remedy?
Install a diesel/water separator?


Thanks y'all!

[Geoff]

You already have a diesel/water fuel separater-- your primary fuel filter.  Sorry, but maybe you need an honest to God Detroit Diesel mechanic to get you through this.

[Ed Hackenbruch]

If you keep your fuel tank full you won't have a problem of water condensation.  

[buswarrior]

Ditto, get help.

Water condensation is the biggest piece of bullshit mythology ever perpetrated on vehicle and boat owners.

Nothing but a lie to cover up the water in the fuel from the pumps.

Since all the advances in fuel storage regulations, decades ago, we don't often get water delivered into our tanks via the pump like the old days. And when we do, someone introduced the water, it didn't "grow" there.

Believe in whichever false prophets you want, if you are really committed, I would love to see a test done to "create" water in a proper vehicle fuel system. Some decent measure of scientific method and the ability to reproduce the results please.

Happy coaching!
Buswarrior

[Ed Hackenbruch]

So i guess that when i get in my car and the windows are all fogged up on the inside that means that somebody has sprayed water on them?     

[buswarrior]

No Ed, the moisture is in the carpet and seating materials. Not the same at all.

Happy coaching!
Buswarrior

[Ed Hackenbruch]

Ummmm......what about the moisture in the air? 

[bevans6]

Day late and a dollar short on the picture of the engine compartment gauge - it's screwed into the end of the oil pressure manifold on the side engine cradle of an MCI.  Definitely not the fuel pressure, you can see the oil pressure sender and the oil pressure switch on the manifold also.